[Q] Best Battery Roms for Samsung galaxy s3

Hi There,
I presently have CM11 Rom for which sucks some how in when it comes down to battery but it's super fast.Are there any other custom Roms for GTI9300 other than CM.
I also have another basic query what is the difference between a rom and a kernel..does kernel add anything to the battery life?
Can i add custom kernels to custom roms??If so can i add custom kernel to the existing CM11 to improve battery life ??

Thanks and looking forward to the answer!